Dynamic fluid seal

ABSTRACT

A low drag fluid seal. The fluid seal includes a lip separated from the rotor shaft, during operation, by a gap, the gap being sufficient narrow, radially, to prevent liquid from seeping through the gap at an unacceptable rate, but sufficiently wide, radially, to avoid unacceptably high viscous drag. Fluid that seeps through the gap accumulates in a recovery cavity and is recovered.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation in part of U.S. applicationSer. No. 15/485,107, filed Apr. 11, 2017, entitled “DYNAMIC FLUID SEAL”,which claims priority to and the benefit of U.S. Provisional ApplicationNo. 62/321,139, filed Apr. 11, 2016, entitled “DYNAMIC FLUID SEAL”; theentire content of both of the applications identified in this paragraphis incorporated herein by reference.

FIELD

One or more aspects of embodiments according to the present inventionrelate to fluid seals, and more particularly to fluid seals for use insystems with high rates of rotation.

BACKGROUND

Rotary shaft seals enable a rotating shaft to pass through an enclosurewhile blocking the flow of a fluid such as oil or water. In some systemsan elastomer of annular shape provides the required sealing function;such seals are commonly referred to as lip seals. For applications wherethe shaft surface speeds are relatively low (e.g. less than 2 m/second),such seals may perform adequately. However, for high speed applications(e.g. greater than 20 m/second), lip seals may encounter severalproblems, including that (i) drag and drag related losses may becomeexcessive, especially when sealing against liquid pressures which aremore than a few kPa, (ii) temperature rise may become excessive, and(iii) the service life of the lip seal may become unacceptably short.

Thus, there is a need for an improved seal for a rotating shaft.

SUMMARY

Aspects of embodiments of the present disclosure are directed toward alow drag fluid seal for an electric motor rotor. In a first embodiment,the fluid seal includes a flexible lip separated from the rotor shaft bya gap, the gap being sufficient narrow, radially, to prevent liquid fromseeping through the gap at an unacceptable rate, but sufficiently wide,radially, to avoid unacceptably high viscous drag. Fluid that seepsthrough the gap accumulates in a recovery cavity and is recovered by ascavenge pump. In a second embodiment, the fluid seal includes aflexible lip separated from the rotor shaft by a gap, the gap beingsufficiently narrow, radially, to prevent liquid from seeping throughthe gap at an unacceptable rate, but sufficiently wide, radially, toavoid unacceptably high viscous drag. Fluid that seeps through the gapaccumulates in a recovery cavity and is recovered by action of positiveair pressure adjacent to the recovery cavity.

According to an embodiment of the present disclosure there is provided arotary fluid coupling system, including: a rotor shaft; a first fluidseal around the rotor shaft; a second fluid seal around the rotor shaft;and a flow cavity located axially between the first fluid seal and thesecond fluid seal and in fluid communication with and overlapping a holein the rotor shaft, the first fluid seal including: a first flexiblelip, a second flexible lip, and a third flexible lip, each surroundingthe rotor shaft; a recovery cavity, positioned axially between the firstflexible lip of the first fluid seal and the second flexible lip of thefirst fluid seal, the recovery cavity of the first fluid seal configuredto recover fluid escaping through a gap between the first flexible lipof the first fluid seal and the rotor shaft; and a first compressed aircavity, between the second flexible lip of the first fluid seal and thethird flexible lip of the first fluid seal, the first compressed aircavity of the first fluid seal being in fluid communication with asource of compressed air through one or more supply holes in the firstfluid seal, the one or more supply holes located between the secondflexible lip of the first fluid seal and the third flexible lip of thefirst fluid seal, the second fluid seal including: a first flexible lipand a second flexible lip surrounding the rotor shaft; and a recoverycavity, positioned between the first flexible lip of the second fluidseal and the second flexible lip of the second fluid seal, the recoverycavity of the second fluid seal configured to recover fluid escapingthrough a gap between the first flexible lip of the second fluid sealand the rotor shaft, wherein the flow cavity is immediately axiallybetween the first flexible lip of the first fluid seal and the firstflexible lip of the second fluid seal.

In one embodiment, the rotary fluid coupling system includes: a thirdflexible lip surrounding the rotor shaft; and a first compressed aircavity, between the first flexible lip of the second fluid seal and thesecond flexible lip of the second fluid seal, the first compressed aircavity of the second fluid seal being in fluid communication with thesource of compressed air.

In one embodiment, the rotary fluid coupling system includes a bearingon the rotor shaft and between the second flexible lip of the secondfluid seal and the first flexible lip of the second fluid seal.

In one embodiment, the rotary fluid coupling system includes a secondcompressed air cavity between the first flexible lip of the second fluidseal and the bearing, the second compressed air cavity being in fluidcommunication with the source of compressed air.

In one embodiment, the rotary fluid coupling system includes a scavengepump having an inlet in fluid communication with the recovery cavity ofthe first fluid seal.

In one embodiment, the second flexible lip of the first fluid seal isconfigured: to flex away from the rotor shaft to form a gap between thesecond flexible lip of the first fluid seal and the rotor shaft when apressure difference exists between a first side of the second flexiblelip of the second fluid seal and a second side of the second flexiblelip of the first fluid seal, a pressure on the first side of the secondflexible lip of the first fluid seal being greater than a pressure onthe second side of the second flexible lip of the first fluid seal; andto contact the rotor shaft when the pressure on the first side of thesecond flexible lip of the first fluid seal is not greater than thepressure on the second side of the second flexible lip of the firstfluid seal.

In one embodiment, the rotary fluid coupling system includes at leastone of: a scavenge pump configured to pump fluid, air, or a combinationof fluid and air from the recovery cavity of the first fluid seal; afluid-air separator; and a main pump.

In one embodiment, the first flexible lip of the first fluid seal isconfigured: to flex away from the rotor shaft to form a gap between thesecond flexible lip of the first fluid seal and the rotor shaft when apressure difference exists between a first side of the second flexiblelip of the second fluid seal and a second side of the second flexiblelip of the first fluid seal, a pressure on the first side of the secondflexible lip of the first fluid seal being greater than a pressure onthe second side of the second flexible lip of the first fluid seal; andto contact the rotor shaft when the pressure on the first side of thesecond flexible lip of the first fluid seal is not greater than thepressure on the second side of the second flexible lip of the firstfluid seal.

According to an embodiment of the present disclosure there is provided arotary fluid coupling system, including: a rotor shaft; a first fluidseal around the rotor shaft; a second fluid seal around the rotor shaft;and a flow cavity located axially between the first fluid seal and thesecond fluid seal and in fluid communication with and overlapping a holein the rotor shaft, the first fluid seal including: a first rigid lip, asecond rigid lip, and a third rigid lip, each surrounding the rotorshaft; a recovery cavity, positioned axially between the first rigid lipof the first fluid seal and the second rigid lip of the first fluidseal, the recovery cavity of the first fluid seal configured to recoverfluid escaping through a gap between the first rigid lip of the firstfluid seal and the rotor shaft; and a first compressed air cavity,between the second rigid lip of the first fluid seal and the third rigidlip of the first fluid seal, the first compressed air cavity of thefirst fluid seal being in fluid communication with a source ofcompressed air through one or more supply holes in the first fluid seal,the one or more supply holes located between the second rigid lip of thefirst fluid seal and the third rigid lip of the first fluid seal, thesecond fluid seal including: a first rigid lip and a second rigid lipsurrounding the rotor shaft; and a recovery cavity, positioned betweenthe first rigid lip of the second fluid seal and the second rigid lip ofthe second fluid seal, the recovery cavity of the second fluid sealconfigured to recover fluid escaping through a gap between the firstrigid lip of the second fluid seal and the rotor shaft, wherein the flowcavity is immediately axially between the first rigid lip of the firstfluid seal and the first rigid lip of the second fluid seal.

In one embodiment, the second fluid seal includes: a third rigid lipsurrounding the rotor shaft; and a first compressed air cavity, betweenthe first rigid lip of the second fluid seal and the second rigid lip ofthe second fluid seal, the first compressed air cavity of the secondfluid seal being in fluid communication with the source of compressedair.

In one embodiment, the rotary fluid coupling system includes a bearingon the rotor shaft and between the second rigid lip of the second fluidseal and the first rigid lip of the second fluid seal.

In one embodiment, the rotary fluid coupling system includes a secondcompressed air cavity between the first rigid lip of the second fluidseal and the bearing, the second compressed air cavity being in fluidcommunication with the source of compressed air.

In one embodiment, the rotary fluid coupling system includes a scavengepump having an inlet in fluid communication with the recovery cavity ofthe first fluid seal.

In one embodiment, the rotary fluid coupling system includes at leastone of: a scavenge pump configured to pump fluid, air, or a combinationof fluid and air from the recovery cavity of the first fluid seal; afluid-air separator; and a main pump.

According to an embodiment of the present disclosure there is provided arotary fluid coupling system, including: a rotor shaft; a first fluidseal around the rotor shaft; a second fluid seal around the rotor shaft;and a flow cavity located axially between the first fluid seal and thesecond fluid seal and in fluid communication with and overlapping a holein the rotor shaft, the first fluid seal including: a first flexible lipsurrounding the rotor shaft; a flexible seal including a second flexiblelip and a third flexible lip, each surrounding the rotor shaft; arecovery cavity, positioned axially between the first flexible lip ofthe first fluid seal and the flexible seal of the first fluid seal, therecovery cavity of the first fluid seal configured to recover fluidescaping through a gap between the first flexible lip of the first fluidseal and the rotor shaft; and a first compressed air cavity, between thesecond flexible lip of the flexible seal and the third flexible lip ofthe flexible seal, the first compressed air cavity of the first fluidseal being in fluid communication with a source of compressed airthrough one or more supply holes in the flexible seal, the one or moresupply holes located between the second flexible lip of the flexibleseal and the third flexible lip of the flexible seal, the second fluidseal including: a first flexible lip, and a second flexible lip, bothsurrounding the rotor shaft; and a recovery cavity, positioned betweenthe first flexible lip of the second fluid seal and the second flexiblelip of the second fluid seal, the recovery cavity of the second fluidseal configured to recover fluid escaping through a gap between thefirst flexible lip of the second fluid seal and the rotor shaft, whereinthe flow cavity is immediately axially between the first flexible lip ofthe first fluid seal and the first flexible lip of the second fluidseal.

According to an embodiment of the present disclosure there is provided arotary fluid coupling system, including: a rotor shaft; a first fluidseal around the rotor shaft; a second fluid seal around the rotor shaft;and a flow cavity located axially between the first fluid seal and thesecond fluid seal and in fluid communication with and overlapping a holein the rotor shaft, the first fluid seal including: a first simple seal,a second simple seal, and a third simple seal, each surrounding therotor shaft; a recovery cavity, positioned axially between the firstsimple seal of the first fluid seal and the second simple seal of thefirst fluid seal, the recovery cavity of the first fluid seal configuredto recover fluid escaping through a gap of the first simple seal of thefirst fluid seal; and a first compressed air cavity, between the secondsimple seal of the first fluid seal and the third simple seal of thefirst fluid seal, the first compressed air cavity of the first fluidseal being in fluid communication with a source of compressed airthrough one or more supply holes in the first fluid seal, the one ormore supply holes located between the second simple seal of the firstfluid seal and the third simple seal of the first fluid seal, the secondfluid seal including: a first simple seal and a second simple sealsurrounding the rotor shaft; and a recovery cavity, positioned betweenthe first simple seal of the second fluid seal and the second simpleseal of the second fluid seal, the recovery cavity of the second fluidseal configured to recover fluid escaping through a gap of the firstsimple seal of the second fluid seal, wherein the flow cavity isimmediately axially between the first simple seal of the first fluidseal and the first simple seal of the second fluid seal.

In one embodiment, the first fluid seal includes a housing element; thefirst simple seal includes a first rigid lip; the second simple sealincludes a second rigid lip; the third simple seal includes a thirdrigid lip; each of the first rigid lip, the second rigid lip, and thethird rigid lip is secured to the housing element or to the rotor shaft;the gap of the first simple seal is between the first rigid lip and thehousing element or the rotor shaft; the second simple seal includes agap is between the second rigid lip and the housing element or the rotorshaft; the third simple seal includes a gap between the third rigid lipand the housing element or the rotor shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will beappreciated and understood with reference to the specification, claims,and appended drawings wherein:

FIG. 1 is a schematic cross-sectional view of a generic lip seal,according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of a seal and bearing assembly on ashaft, according to an embodiment of the present invention;

FIG. 3 is a cross-sectional and schematic view of a rotary fluidcoupling system, according to an embodiment of the present invention;

FIG. 4 is an exploded cutaway view of a seal and bearing assembly and anelectric motor end bell, according to an embodiment of the presentinvention;

FIG. 5 is a cutaway perspective view of a seal and bearing assembly,according to an embodiment of the present invention;

FIG. 6 is a perspective view of a seal and bearing assembly, accordingto an embodiment of the present invention;

FIG. 7 is a cutaway perspective view of an electric motor rotor and twoseal and bearing assemblies, according to an embodiment of the presentinvention;

FIG. 8 is a cross-sectional view of a seal and bearing assembly on ashaft, according to an embodiment of the present invention;

FIG. 9 is a cross-sectional view of a seal and bearing assembly on ashaft, according to an embodiment of the present invention;

FIG. 10 is a cross-sectional view of a seal and bearing assembly on ashaft, according to an embodiment of the present invention;

FIG. 11 is a cross-sectional view of a seal and bearing assembly on ashaft, according to an embodiment of the present invention; and

FIG. 12 is a cross-sectional view of a seal and bearing assembly on ashaft, according to an embodiment of the present invention.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of adynamic fluid seal provided in accordance with the present invention andis not intended to represent the only forms in which the presentinvention may be constructed or utilized. The description sets forth thefeatures of the present invention in connection with the illustratedembodiments. It is to be understood, however, that the same orequivalent functions and structures may be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of the invention. As denoted elsewhere herein, like elementnumbers are intended to indicate like elements or features.

FIG. 1 shows a fluid seal 105 around a shaft 160. In some embodimentsliquid is present on a fluid side 210 of the seal, and air is present onan air side 220 of the seal (for example, as a result of the air sidebeing open to the atmosphere). In other embodiments, fluids (e.g.,fluids at two different pressures) may be present on both sides of thefluid seal 105, or air (e.g., air at two different pressures) may bepresent on both sides of the fluid seal 105. Drag may be due mainly tofluid viscosity effects in the thin fluid layer between the respectivesurfaces of the fluid seal 105 and shaft 160. In FIG. 1, D is the shaftdiameter, g is the thickness of the fluid layer (i.e., the radialdimension of the gap between the lip of the seal and the outer surfaceof the shaft 160), L is the length of the contact (or near-contact)region (i.e., the axial extent of the gap), μ is the fluid dynamicviscosity, and ω is the angular shaft speed. The shaft surface speed isequal to ωD/2. Viscous shear pressure is equal to dynamic viscositytimes the gradient of shear velocity, or μωD/(2g). The tangential dragforce, F_(t), is equal to the shear pressure times the contact area.Hence, F_(t)=πμωD²L/(2g). The drag torque, T_(d), is D/2 times thetangential drag force. Hence:T _(d) =πμωD ³ L/(4g).  (1)

To reduce the drag torque, D, or L, or both, may be made as small aspossible, and g may be made as large as possible. D may however beconstrained to be adequately large to safely handle maximum torquelevels and to meet stiffness requirements. While L, the length of thecontact (or near-contact) region, may be held to a relatively smallvalue, there are practical limits based on seal life and fabricationcapabilities, and as the seal wears, L may increase. For a conventionalflexible lip seal, g is inherently small and is based on inherentsurface and fluid properties (g may be on the order of a few microns).If g is in some way forced to increase beyond these values, fluidleakage may occur.

Providing seals for liquid-cooled, high-speed, electric motor rotors maybe challenging. To inject and recover coolant (i.e., cooling fluid) fromthe rotor, typically four seals are required. Furthermore, for suchmotors, the space available for seals may be quite small. Someembodiments address the challenges present in such motors, and provide ashaft seal which produces relatively low drag for high speedapplications (e.g., less than 0.02 Nm for a 25 mm diameter shaftrotating at 20,000 rpm with fluid head of 70 kPa or greater).

From Equation (1) it may be seen that as g (the radial dimension of thegap) is increased, drag torque is reciprocally reduced. As g isincreased beyond the micron range, however, leakage may occur.Accordingly, some embodiments provide a seal for which the drag isrelatively small and the fluid leakage rate is nonetheless sufficientlysmall that the pumping power associated with leak recovery isacceptable. The ratio between the head loss associated with inertialeffects and head loss associated with viscous effects may be known asthe Reynolds number. When the Reynolds number is much larger than unity,the head loss may be due mainly to inertial effects, and viscosity maybe neglected. When the Reynolds number is small compared with unity, thereverse may be true, and flow may be calculated based on viscosity,while neglecting inertial effects. For a fluid seal, the Reynolds numbermay be on the order of 0.01 and hence a viscosity-based calculation maybe used.

The following equation may be used to calculate the leakage flow, F, asa function of the fluid pressure, P, across the seal, the fluidviscosity, μ, and the geometric parameters shown FIG. 1:F=πDg ³ P/(12 μL)  (2)

A seal may then be designed, and/or its characteristics may be analyzed,using Equation (1) and Equation (2). For example, the followingparameters may be applicable to one embodiment:

D=25 mm=0.025 m

L=2.54 mm=0.00254 m

P=10 psi=70,000 Pa

μ₁=0.05 Pa-seconds (which may correspond to the dynamic viscosity oftransformer oil at 20° C.)

μ₂=0.01 Pa-seconds (which may correspond to the dynamic viscosity oftransformer oil at 60° C.)

For these parameters, the worst case drag may be calculated usingEquation (1), using the higher value of viscosity, i.e., using μ₁, whichis for transformer oil at 20° C. Assuming that the maximum acceptabledrag torque at 20,000 rpm (2093 rad/second) is 0.05 Nm, solving Equation(1) for g under these conditions provides g=0.0684 mm (0.00269″). Forhigher temperatures, coolant viscosity and drag may be less. The worstcase leakage may take place when the coolant is at maximum temperature(e.g., at 60° C.), at which the dynamic velocity may be μ₂=0.01Pa-seconds. Using this viscosity, setting g equal to 0.0684 mm, andsetting P=70,000 Pa, Equation (2) provides a flow rate of 0.00000586m/second=0.35 liters per minute. This flow rate may be handled by asmall pump. The theoretical pumping power (i.e., the power required topump the fluid across the 70,000 Pa head) is only 0.41 W. At lower headsand lower temperatures, flow and pumping power may be even less. In someembodiments the gap may have a radial dimension greater than 0.005 mmand less than 0.5 mm, and an axial extent greater than 0.5 mm and lessthan 20 mm. The shaft may have a diameter greater than 5 mm and lessthan 100 mm.

As used herein, the term “fluid” may describe a liquid or a gas oreither, unless context indicates otherwise (e.g., in the term “fluid-airseparator”, fluid refers to a liquid). In some embodiments the fluid isa cooling fluid, or a lubricating fluid, or a fluid (e.g., automatictransmission fluid) suitable for performing both cooling andlubrication. In the claims, “fluid” means liquid, except in the phrase“in fluid communication” in which it means either liquid or gas. In aseal, with one or more lips, that separates a fluid (e.g., a liquid) onone side from air (e.g., the atmosphere) on the other side, the “fluidside” of any lip (or of the seal) is the side facing toward the fluid,and the “air side” of any lip (or of the seal) is the side facing towardthe air.

Seals according to FIG. 1 may be combined, for example to form a rotaryfluid coupling for communicating a liquid (e.g. oil) between astationary environment and a rotating shaft, as illustrated in FIG. 2.Fluid is supplied to a flow cavity 114, e.g., through a radial hole 126(FIG. 3), and from the flow cavity 114 it may flow into the shaftthrough a radial hole 162 (FIG. 3). The rotary fluid coupling includes afirst fluid seal, to the right of the flow cavity 114, and a secondfluid seal, to the left of the flow cavity 114, each of these two fluidseals acting as an obstacle to the escape of fluid from the flow cavity114. The first fluid seal includes a first fluid-side lip 106Bimmediately to the right of the flow cavity 114, a first air-side lip112A, to the right of, i.e., on the air side of, the first fluid-sidelip 106B, and a first compressed air lip 112B, to the right of, i.e., onthe air side of, the first air-side lip 112A. Each of the first air-sidelip 112A and the first compressed air lip 112B may be a flexible lip;these two lips may be fabricated together, as a single part, as shown.The first fluid-side lip 106B is separated from the outer surface of theshaft 160 by a sufficiently small gap (a first fluid-side gap) thatseepage of liquid through the first fluid-side gap, from the flow cavity114 to a first recovery cavity 125 (from which the seeped fluid may berecovered, as described in further detail below), is small. In someembodiments the first fluid-side lip 106B is configured to flex underfluid pressure such that a desired gap is established, the radialdimension of which may be a function of the fluid pressure, and whichmay vary from zero (i.e., with the first fluid-side lip 106B in contactwith the shaft), and, e.g., as much as 0.5 mm. The recovery cavity 125is “positioned between” the first fluid-side lip 106B and the firstcompressed air lip 112B, and the recovery cavity 125 is “immediatelyaxially between” the first fluid-side lip 106B and the first air-sidelip 112A. The assembly that surrounds and supports the shaft in FIG. 2(i.e., the assembly of parts illustrated in FIG. 2 except the shaft) maybe referred to as a seal and bearing assembly 101.

Compressed air is supplied to a first compressed air cavity 123, fromwhich it seeps through the gap between the first air-side lip 112A andthe surface of the shaft 160, to (i) prevent liquid from seeping throughthe same gap, in the opposite direction, and (ii) to drive liquid out ofthe first recovery cavity 125 through one or more first liquid recoveryholes 128 (FIGS. 3 and 5) through which the liquid returns to afluid-air separator 168 (FIG. 3) or to a reservoir. A scavenge pump 165(FIG. 3) may also be employed to evacuate the first recovery cavity 125.In some embodiments the flow of compressed air is sufficient to driveliquid out of the first recovery cavity 125, and the scavenge pump 165may be absent. The air pump 172 or “compressor” (FIG. 3) handles aironly; this may simplify the pump design, over that of the scavenge pump165, which may handle a combination of air and liquid. Pumping powerlevels may be very small, e.g., on the order of 1.0 W, if the shaftdiameter is on the order of 25 mm.

Each of the first air-side lip 112A and the first compressed air lip112B may be in contact with the shaft 160 when compressed air is notsupplied to the first compressed air cavity 123, and, in operation, thecompressed atmospheric air supplied to the first compressed air cavity123 may be supplied under sufficient pressure to cause a small gap toform between each of first air-side lip 112A and the first compressedair lip 112B (both of which may be soft or flexible lip seals) and theshaft 160.

In some embodiments, the second fluid seal includes a second fluid-sidelip 106A immediately to the left of the flow cavity 114, a secondair-side lip 110B, to the left of, i.e., on the air side of, the secondfluid-side lip 106A, and a second compressed air lip 110A, to the leftof, i.e., on the air side of, the second air-side lip 110B. In additionto being supplied to the first compressed air cavity 123, compressedatmospheric air is supplied to second and third compressed air cavities122, 119. This compressed air may be supplied through one or more airsupply holes 129, 133 (FIG. 5) opening into the compressed air cavities123, 122, 119. The operation of the second fluid seal is similar to thatof the first fluid seal, except that the second fluid seal includes abearing 124 (e.g., a ball bearing) between the second fluid-side lip106A and the second air-side lip 110B. The compressed air supplied tothe third compressed air cavity 119 (which is between the secondfluid-side lip 106A and the bearing 124) drives liquid (that seepsthrough the second fluid-side gap between second fluid-side lip and theouter surface of the shaft 160) through the bearing into the secondrecovery cavity 120, from which it is driven (by the positive pressuresupplied from the second and third compressed air cavities 122, 119 oneither side of it) back to a liquid reservoir or fluid-air separator.

The connection from the air supply channel to the third compressed aircavity 119 may be an orifice sized to provide liquid and air to thebearing in a proportion suitable for adequate lubrication withoutproducing excessive viscous drag. In some embodiments, the orifice has adiameter of about 1 mm. In other embodiments, the diameter may besmaller, e.g., as small as 0.2 mm or smaller, or it may be larger e.g.,as large as 1.5 mm or larger. The first recovery cavity 125 and thesecond recovery cavity 120 may be connected to a liquid reservoir by achannel or other liquid recovery passage, e.g., a line 163, (which maybe a pipe or tube as shown in FIG. 3), allowing liquid and air to returnto the liquid reservoir or to the fluid-air separator (which may alsoact as a liquid reservoir).

In some embodiments, the rotary fluid coupling of FIG. 2 includes afirst seal housing element 104 that is press fitted within a bore in theelectric motor end bell 150 (FIG. 4), and a second seal housing element102 that is press fitted to the bearing outer race and that slip fitswithin the end bell bore, and is sealed to the end bell bore by anO-ring 148.

The embodiment of FIG. 2 may provide low drag, as well as furtheradvantages. For example, shaft drag loss may be quite small, e.g., lessthan 10 W, for a 25 mm shaft rotating at 20,000 rpm. Foreign materialmay prevented from entering the first and second recovery cavities 125,120 during non-operation by action of the outer lip seals (e.g., as aresult of the first and second compressed air lips 112B, 110A and/or thefirst and second air-side lips 112A, 110B being in contact with theshaft 160 during non-operation), and during operation by action ofpositive air pressure applied to the outer compressed air cavities,i.e., the first and second compressed air cavities 123, 122. Duringoperation, lip seal contact with the shaft may be eliminated by actionof air flow. This may significantly reduce both lip seal wear andmechanical drag during operation. Bearing lubrication may be provided bya combination of leakage liquid (e.g., oil) and limited air flow whichenters the third compressed air cavity 119. The ratio of air flow to oilflow may be controlled such that lubrication is optimized. It will beunderstood that the rotary fluid coupling of FIG. 2 may be used eitheron the pump end of the shaft or on the recovery end of the shaft, andthe fluid may flow from the flow cavity 114 into the shaft, or from theshaft into the flow cavity. The respective rates of air and liquidleakage may be calculated using Equation (2).

FIG. 3 shows a sectional view of a rotary fluid coupling according toone embodiment, with the cutting plane selected to pass through a firstpair of radial holes 162 in the shaft 160, an axial hole 164 in theshaft 160, a second pair of radial holes 166 in the shaft 160, liquidrecovery holes 128, 130, air supply holes 129, 133, and axial passages,or “flow slots” 142, 144 (described in further detail below) providingaxial connections between and to these radial holes. The scavenge pump165 (which in some embodiments is absent) evacuates the first and secondrecovery cavities 125, 120 into the fluid-air separator 168, a main pump250 draws fluid from the bottom of the fluid-air separator 168 and pumpsit back into the flow cavity 114 (either at the end of the shaft 160shown or at the opposite end). The air pump 172 provides compressed airto the compressed air cavities 123, 122, 119 (FIG. 2). In the embodimentillustrated in FIG. 3 the radial holes 162, 166 in the shaft 160 arethrough holes (i.e., pairs of holes separated azimuthally by 180degrees) and the liquid recovery holes 128, 130 and the recovery flowslot 144 are separated azimuthally by 180 degrees from the air supplyholes 129, 133 and the compressed air flow slot 142; in otherembodiments the azimuthal separations may be different, so that a crosssection taken with a cutting plane through the central axis of thesystem would not show all of these passages and holes simultaneously.

FIG. 4 is an exploded view of (i) a perspective view of an electricmotor end bell 150 and (ii) an exploded cutaway view of the seal andbearing assembly 101, according to one embodiment. Fluid flowing to orfrom the flow cavity 114 (FIG. 3) flows radially through one or moreradial end bell fluid holes 152, compressed air flowing to thecompressed air cavities 123, 122, 119 flows through one or more radialend bell compressed air holes 153, and fluid and/or air from therecovery cavities 125, 120 (FIG. 2) flows through one or more radial endbell recovery holes 154. Air or fluid that flows radially through theradial end bell holes 152, 153, 154 flows axially through flow slots,such as the fluid flow slot 140 illustrated, or compressed air flowslots 142 (FIG. 5) or recovery flow slots 144 (FIG. 5), and from eachflow slot into or out of one or more corresponding radial holes (e.g.,liquid recovery holes 128, 130, or air supply holes 129, 133) in theseal and bearing assembly 101. If a radial end bell hole 152, 153, 154is axially aligned with a corresponding radial hole in the seal andbearing assembly 101, a flow slot may not be needed. If there is anazimuthal misalignment between a radial end bell hole 152, 153, 154 anda corresponding radial hole in the seal and bearing assembly 101, anazimuthal flow slot may be used, and if a radial end bell hole 152, 153,154 and a corresponding radial hole in the seal and bearing assembly 101are misaligned both axially and azimuthally then a flow slot that isneither entirely axial nor entirely azimuthal (e.g., a flow slot that ishelical, or that has an axial portion and an azimuthal portion) may beused.

FIG. 5 is a cutaway perspective view showing features described aboveand illustrated in FIGS. 2 and 3. FIG. 6 is a perspective exterior viewof the seal and bearing assembly 101, showing a compressed air flow slot142, two fluid flow slots 140, a recovery flow slot 144, and the O-ring148.

FIG. 7 depicts a liquid-cooled motor rotor according to one embodiment,and a pair of rotary fluid couplings, each of which includes a seal andbearing assembly 101. Fluid flows into a first axial hole 164 (FIG. 3;not visible in FIG. 7) in the motor rotor shaft 160 at a first rotaryfluid coupling including a first seal and bearing assembly 101A, at afirst end of the motor rotor. The fluid then flows generally axiallythrough the motor rotor and back out of the motor rotor shaft at asecond rotary fluid coupling (at a second end of the motor rotor)including a second seal and bearing assembly 101B. In other embodimentsthe fluid flows in the opposite direction. Each of the seal and bearingassemblies 101A, 101B illustrated in FIG. 7 has (like the seal andbearing assembly of FIG. 6) first and second compressed air lips thatare flexible lips; the remainder of the lips are also flexible anddeform in response to fluid pressure such that a controlled gap isestablished. In other embodiments, other combinations of flexible lipsmay be used. In some embodiments, the non-drive end of the shaft 160 mayhave a significantly smaller diameter, and may have a rotary fluidcoupling with simple (single) lip seals.

Within the motor rotor, the fluid flows through the first axial hole 164(as mentioned above), exits the motor rotor shaft through one or moreradial holes 166 in the shaft 160 and flows through radial ports 173located in a rotor end plate 171 at the first end of the motor rotor.After passing through the body of the rotor (e.g., through coolingpassages in the laminations of the rotor), fluid then passes throughradial ports 173 located in a rotor end plate 171 at the second end ofthe motor rotor, through radial holes 166 in the shaft 160 to a secondaxial hole 164 at the second end of the motor rotor, and back out of themotor rotor shaft at a second rotary fluid coupling. The fluid exitingthe second fluid coupling may return to a reservoir or to the fluid-airseparator 168.

FIG. 8 shows a fluid coupling which is similar to that of FIG. 2, butwhere the first air side lip 175A and the second air side lip 177B arerigid as opposed to flexible. In many cases, this may not providebenefit as mechanical tolerances may be more demanding and fabricationcosts may be higher. However, in a some cases, rigid compressed air lipsmay be beneficial. One such case may be where more constant air flowrates between compressed air and recovery cavities are desired. With arigid lip, the gap between the lip and the shaft will remain relativelyconstant with variations in temperature and air pressure—which in turnmeans that air flow will vary less with changes in temperature and airpressure. Another benefit is that a rigid lip may have a greater lifethan a flexible lip—especially in the case where the compressed air mayinclude corrosive chemicals which could cause a flexible lip to degradeover time.

FIG. 9 is yet another embodiment of the FIG. 2 configuration, but wherethe first air side lip 175A, the second air side lip 177B, the firstcompressed air lip 175B, and the second compressed air lip 177A are allrigid lips. The issues and benefits for the FIG. 9 configuration aresimilar to those of the FIG. 8 configuration. Each rigid lip may be anintegral part of the first seal housing element 104 or of the secondseal housing element 102, as shown for example in FIGS. 8 and 9. Eachflexible seal may be a separate element that may, for example, bepressed into the first seal housing element 104 or the second sealhousing element 102, as shown for the first and second compressed airlips 112B, 110A in FIG. 8. In some embodiments, two or more adjacentflexible lips are part of a single monolithic element that may, forexample, be pressed into the first seal housing element 104 or thesecond seal housing element 102, as shown, in FIGS. 8 and 9, for thefirst and second fluid-side lips 106B, 106A. In some embodiments, arigid lip, or a monolithic element including more than one rigid lip,may similarly be pressed into the first seal housing element 104 or thesecond seal housing element 102, instead of such a lip or such lipsbeing an integral part of, or being integral parts of, the first sealhousing element 104 or the second seal housing element 102.

FIG. 10 shows an embodiment in which all of the lips of both the firstfluid seal and the second fluid seal are rigid, including the firstfluid-side lip 178B and the second fluid-side lip 178A, and the lipsthat are rigid in the embodiment of FIG. 9, i.e., the first air side lip175A, the second air side lip 177B, the first compressed air lip 175B,and the second compressed air lip 177A.

As shown in FIGS. 2 and 3, fluid flows through the flow cavity 114 andthrough radial holes 162 in the shaft 160 to flow into or out of anaxial hole 164 in the shaft 160. A first fluid seal includes a firstfluid side lip 106B and a first air-side lip 112A, each of which may bea flexible lip. A uniform gap, or “fluid-side gap” is formed between thefirst fluid side lip 106B and the shaft 160, with a radial dimensionequal to g₁. The shaft diameter is D, the length of the first fluid sidelip 106B is L₁, and the fluid pressure of the liquid, relative toatmospheric, is P₀. The first fluid side lip 106B and the first air-sidelip 112A form, between them, a first recovery cavity 125 in which (inthe embodiment of FIG. 3) a partial vacuum is maintained by action of ascavenge pump 165 (which may be a relatively small pump). The gap, or“air-side gap” associated with the first air-side lip 112A is g₂, andthe length of the first air-side lip 112A is L₂. Drag torque associatedwith the first air-side lip 112A may be negligible since the air-sidegap is filled with air, the viscosity of which may be about onethousandth that of typical liquids.

To reduce air flow through the air-side gap, g₂ may be maintained assmall as possible. If g₂ is held at 0.025 mm (0.001″), and a vacuum of7000 Pa (1 psi) is maintained, air flow, as calculated by Equation (2)(using μ=0.00002 Pa-seconds), is about 3 liters per minute for a shaftdiameter of 25 mm; air velocity through g₂ is approximately 25 m/second.The associated theoretical pumping power is 0.35 W. Scavenge flowconsists of a mixture of fluid and air. In a manner similar to thatillustrated in FIG. 3, a fluid-air separator 168 may be used to separateair from the fluid. This separator may be connected such that it servesto also remove air from the primary flow. A main pump 250 may drawliquid from the bottom of the fluid-air separator. Alternatively, thefluid-air separator can be connected such that it deals only with thescavenge flow and is not involved with the primary flow. In someembodiments, the scavenge flow (which, as mentioned above, consists of amixture of fluid and air) may flow directly into a fluid-air separatorwithout first flowing through a pump. In this embodiment the separatormay be a sealed container the interior of which is at a pressure lowerthan atmospheric pressure. The container may have an inlet (connected toone or more recovery cavities) for receiving the scavenge flow, an airoutlet, at or near the top of the container, evacuated by an air pump,and a fluid outlet, at or near the bottom of the container, evacuated bya fluid pump.

In some embodiments, the first air-side lip 112A is a flexible lip thatflexes or deflects into the first recovery cavity 125 when a partialvacuum is present in the first recovery cavity 125, such that a smallair-side gap, g₂ is formed and a small air ingress occurs which preventsfluid escape through g₂, and which also avoids contact, duringoperation, between the flexible first air-side lip 112A and the shaft160. The actual size of g₂ is determined by the stiffness of theflexible first air-side lip 112A and the rate of air flow through g₂. Insome embodiments the flexible first air-side lip 112A does not encounterfrictional wear as contact with the shaft occurs only when the shaft isat rest. Furthermore, since the flexible first air-side lip 112A is notin contact with the shaft during rotation, there is virtually no dragassociated with the flexible first air-side lip 112A; the only drag isdue to air viscosity within g₂. The first air-side lip 112A lip mayhowever be in contact with the shaft when the scavenge pump is notoperated and differential air pressure is zero. This feature may be usedto prevent fluid leakage when the system is not operating, i.e., whenthe shaft rotation rate and fluid pressure are both zero.

The scavenge pump 165 associated with the embodiments of FIG. 3 mayinclude (e.g., consist of) the combination of a fixed displacement pumpand a DC brushless electric motor. As such, the pump flow rate may becontrolled by controlling the speed of the brushless motor. In theembodiment of FIG. 3, the flow rate of the scavenge pump may largelydetermine the size of the gap g₂.

In some embodiments the bearing is full of fluid. In other embodiments,a vent passage with a flow control orifice may allow air from inside themachine (which may be an electric motor) to flow into the space betweenthe inner and outer races of the bearing, and the space between theinner and outer races of the bearing may include air and fluid, with aproportion of fluid that is sufficient for lubrication without producingunacceptable levels of viscous drag.

It will be understood that in any of the embodiments described herein, arigid lip may be substituted for any flexible lip, or a flexible lip maybe substituted for any rigid lip, and that some or all of the functionof the embodiment may be preserved (excluding, for example, the functionof flexing under the effect of a pressure difference on the two sides ofthe lip, and losing contact with the shaft, which may not be present ifa rigid lip is substituted for a flexible lip).

Referring to FIGS. 11 and 12, in some embodiments one or more of thegaps of a fluid seal may, instead of being formed by a lip secured to(or integral with) a housing element and surrounding a shaft, be formedby a lip secured to (or integral with) the shaft and extending nearly tothe surface of a bore in the housing element, or otherwise by gapsformed by changes, along the axial direction, in the inner diameter ofthe housing bore or the outer diameter of the shaft, or both. In theembodiment of FIG. 11, for example, the flow cavity 116 is acircumferential channel in the shaft and a fluid seal is formed on eachside of the flow cavity 116 by a respective small gap between an outersealing surface 107 and the inner sealing surface 108 (which, as shown,is interrupted by the channel forming the flow cavity 116). The outersealing surface 107 and the inner sealing surface 108 may becylindrical, or they may be conical as illustrated in FIG. 11. In theembodiment of FIG. 12, a fluid seal is formed on each side of the flowcavity 114 by lips that are secured to (e.g., integral with) the shaft,each of which extends nearly to the inner surface of a bore in the firstseal housing element 104.

As used herein, a “simple seal” is a structure having a gap (e.g., a gaphaving a transverse dimension of between 0.0001 inches and 0.005 inches,e.g., a transverse dimension that is within a factor of 3 of 0.001inches) that presents an obstacle to fluid flow between a fluid volume(e.g., a first cavity) on one side of the gap and a fluid volume (e.g.,a second cavity, or the atmosphere on the outside of a machine) on theother side of the gap. As such, in FIG. 11, each of the flexible lips110A, 110B, 112A, 112B forms, together with the outer surface of theshaft with which it forms a small gap, a simple seal. Similarly, theouter sealing surface 107 and the inner sealing surface 108 togetherform two simple seals, one on either side of the flow cavity 116. Thegap between the flow cavity 116 and the first recovery cavity 125, forexample, presents an obstacle to fluid flow between the flow cavity 116and the first recovery cavity 125. As used herein, the “transversedimension” of a gap is the smallest distance, in the region of the gap,between the two surfaces between which the gap is formed. A “fluid seal”as used herein, may include one or more simple seals. For example, afirst fluid seal of the embodiment of FIG. 11 includes the three simpleseals shown to the right of the flow cavity 116.

Although exemplary embodiments of a dynamic fluid seal have beenspecifically described and illustrated herein, many modifications andvariations will be apparent to those skilled in the art. Accordingly, itis to be understood that a dynamic fluid seal constructed according toprinciples of this invention may be embodied other than as specificallydescribed herein. The invention is also defined in the following claims,and equivalents thereof.

What is claimed is:
 1. A rotary fluid coupling system, comprising: arotor shaft; a first fluid seal around the rotor shaft; a second fluidseal around the rotor shaft; and a flow cavity located axially betweenthe first fluid seal and the second fluid seal and in fluidcommunication with and overlapping a hole in the rotor shaft, the firstfluid seal including: a first flexible lip, a second flexible lip, and athird flexible lip, each surrounding the rotor shaft; a recovery cavity,positioned axially between the first flexible lip of the first fluidseal and the second flexible lip of the first fluid seal, the recoverycavity of the first fluid seal configured to recover fluid escapingthrough a gap between the first flexible lip of the first fluid seal andthe rotor shaft; and a first compressed air cavity, between the secondflexible lip of the first fluid seal and the third flexible lip of thefirst fluid seal, the first compressed air cavity of the first fluidseal being in fluid communication with a source of compressed airthrough one or more supply holes in the first fluid seal, the one ormore supply holes located between the second flexible lip of the firstfluid seal and the third flexible lip of the first fluid seal, thesecond fluid seal including: a first flexible lip and a second flexiblelip surrounding the rotor shaft; and a recovery cavity, positionedbetween the first flexible lip of the second fluid seal and the secondflexible lip of the second fluid seal, the recovery cavity of the secondfluid seal configured to recover fluid escaping through a gap betweenthe first flexible lip of the second fluid seal and the rotor shaft,wherein the flow cavity is immediately axially between the firstflexible lip of the first fluid seal and the first flexible lip of thesecond fluid seal.
 2. The rotary fluid coupling system of claim 1, thesecond fluid seal further comprising: a third flexible lip surroundingthe rotor shaft; and a first compressed air cavity, between the firstflexible lip of the second fluid seal and the second flexible lip of thesecond fluid seal, the first compressed air cavity of the second fluidseal being in fluid communication with the source of compressed air. 3.The rotary fluid coupling system of claim 2, further comprising abearing on the rotor shaft and between the second flexible lip of thesecond fluid seal and the first flexible lip of the second fluid seal.4. The rotary fluid coupling system of claim 3, the second fluid sealfurther comprising a second compressed air cavity between the firstflexible lip of the second fluid seal and the bearing, the secondcompressed air cavity being in fluid communication with the source ofcompressed air.
 5. The rotary fluid coupling system of claim 1, furthercomprising a scavenge pump having an inlet in fluid communication withthe recovery cavity of the first fluid seal.
 6. The rotary fluidcoupling system of claim 1, wherein the second flexible lip of the firstfluid seal is configured: to flex away from the rotor shaft to form agap between the second flexible lip of the first fluid seal and therotor shaft when a pressure difference exists between a first side ofthe second flexible lip of the second fluid seal and a second side ofthe second flexible lip of the first fluid seal, a pressure on the firstside of the second flexible lip of the first fluid seal being greaterthan a pressure on the second side of the second flexible lip of thefirst fluid seal; and to contact the rotor shaft when the pressure onthe first side of the second flexible lip of the first fluid seal is notgreater than the pressure on the second side of the second flexible lipof the first fluid seal.
 7. The rotary fluid coupling system of claim 1,further comprising at least one of: a scavenge pump configured to pumpfluid, air, or a combination of fluid and air from the recovery cavityof the first fluid seal; a fluid-air separator; and a main pump.
 8. Therotary fluid coupling system of claim 1, wherein the first flexible lipof the first fluid seal is configured: to flex away from the rotor shaftto form a gap between the second flexible lip of the first fluid sealand the rotor shaft when a pressure difference exists between a firstside of the second flexible lip of the second fluid seal and a secondside of the second flexible lip of the first fluid seal, a pressure onthe first side of the second flexible lip of the first fluid seal beinggreater than a pressure on the second side of the second flexible lip ofthe first fluid seal; and to contact the rotor shaft when the pressureon the first side of the second flexible lip of the first fluid seal isnot greater than the pressure on the second side of the second flexiblelip of the first fluid seal.
 9. A rotary fluid coupling system,comprising: a rotor shaft; a first fluid seal around the rotor shaft; asecond fluid seal around the rotor shaft; and a flow cavity locatedaxially between the first fluid seal and the second fluid seal and influid communication with and overlapping a hole in the rotor shaft, thefirst fluid seal including: a first rigid lip, a second rigid lip, and athird rigid lip, each surrounding the rotor shaft; a recovery cavity,positioned axially between the first rigid lip of the first fluid sealand the second rigid lip of the first fluid seal, the recovery cavity ofthe first fluid seal configured to recover fluid escaping through a gapbetween the first rigid lip of the first fluid seal and the rotor shaft;and a first compressed air cavity, between the second rigid lip of thefirst fluid seal and the third rigid lip of the first fluid seal, thefirst compressed air cavity of the first fluid seal being in fluidcommunication with a source of compressed air through one or more supplyholes in the first fluid seal, the one or more supply holes locatedbetween the second rigid lip of the first fluid seal and the third rigidlip of the first fluid seal, the second fluid seal including: a firstrigid lip and a second rigid lip surrounding the rotor shaft; and arecovery cavity, positioned between the first rigid lip of the secondfluid seal and the second rigid lip of the second fluid seal, therecovery cavity of the second fluid seal configured to recover fluidescaping through a gap between the first rigid lip of the second fluidseal and the rotor shaft, wherein the flow cavity is immediately axiallybetween the first rigid lip of the first fluid seal and the first rigidlip of the second fluid seal.
 10. The rotary fluid coupling system ofclaim 9, the second fluid seal further comprising: a third rigid lipsurrounding the rotor shaft; and a first compressed air cavity, betweenthe first rigid lip of the second fluid seal and the second rigid lip ofthe second fluid seal, the first compressed air cavity of the secondfluid seal being in fluid communication with the source of compressedair.
 11. The rotary fluid coupling system of claim 10, furthercomprising a bearing on the rotor shaft and between the second rigid lipof the second fluid seal and the first rigid lip of the second fluidseal.
 12. The rotary fluid coupling system of claim 11, the second fluidseal further comprising a second compressed air cavity between the firstrigid lip of the second fluid seal and the bearing, the secondcompressed air cavity being in fluid communication with the source ofcompressed air.
 13. The rotary fluid coupling system of claim 9, furthercomprising a scavenge pump having an inlet in fluid communication withthe recovery cavity of the first fluid seal.
 14. The rotary fluidcoupling system of claim 9, further comprising at least one of: ascavenge pump configured to pump fluid, air, or a combination of fluidand air from the recovery cavity of the first fluid seal; a fluid-airseparator; and a main pump.
 15. A rotary fluid coupling system,comprising: a rotor shaft; a first fluid seal around the rotor shaft; asecond fluid seal around the rotor shaft; and a flow cavity locatedaxially between the first fluid seal and the second fluid seal and influid communication with and overlapping a hole in the rotor shaft, thefirst fluid seal including: a first flexible lip surrounding the rotorshaft; a flexible seal including a second flexible lip and a thirdflexible lip, each surrounding the rotor shaft; a recovery cavity,positioned axially between the first flexible lip of the first fluidseal and the flexible seal of the first fluid seal, the recovery cavityof the first fluid seal configured to recover fluid escaping through agap between the first flexible lip of the first fluid seal and the rotorshaft; and a first compressed air cavity, between the second flexiblelip of the flexible seal and the third flexible lip of the flexibleseal, the first compressed air cavity of the first fluid seal being influid communication with a source of compressed air through one or moresupply holes in the flexible seal, the one or more supply holes locatedbetween the second flexible lip of the flexible seal and the thirdflexible lip of the flexible seal, the second fluid seal including: afirst flexible lip, and a second flexible lip, both surrounding therotor shaft; and a recovery cavity, positioned between the firstflexible lip of the second fluid seal and the second flexible lip of thesecond fluid seal, the recovery cavity of the second fluid sealconfigured to recover fluid escaping through a gap between the firstflexible lip of the second fluid seal and the rotor shaft, wherein theflow cavity is immediately axially between the first flexible lip of thefirst fluid seal and the first flexible lip of the second fluid seal.16. A rotary fluid coupling system, comprising: a rotor shaft; a firstfluid seal around the rotor shaft; a second fluid seal around the rotorshaft; and a flow cavity located axially between the first fluid sealand the second fluid seal and in fluid communication with andoverlapping a hole in the rotor shaft, the first fluid seal including: afirst simple seal, a second simple seal, and a third simple seal, eachsurrounding the rotor shaft; a recovery cavity, positioned axiallybetween the first simple seal of the first fluid seal and the secondsimple seal of the first fluid seal, the recovery cavity of the firstfluid seal configured to recover fluid escaping through a gap of thefirst simple seal of the first fluid seal; and a first compressed aircavity, between the second simple seal of the first fluid seal and thethird simple seal of the first fluid seal, the first compressed aircavity of the first fluid seal being in fluid communication with asource of compressed air through one or more supply holes in the firstfluid seal, the one or more supply holes located between the secondsimple seal of the first fluid seal and the third simple seal of thefirst fluid seal, the second fluid seal including: a first simple sealand a second simple seal surrounding the rotor shaft; and a recoverycavity, positioned between the first simple seal of the second fluidseal and the second simple seal of the second fluid seal, the recoverycavity of the second fluid seal configured to recover fluid escapingthrough a gap of the first simple seal of the second fluid seal, whereinthe flow cavity is immediately axially between the first simple seal ofthe first fluid seal and the first simple seal of the second fluid seal.17. The rotary fluid coupling system of claim 16, wherein: the firstfluid seal comprises a housing element; the first simple seal of thefirst fluid seal comprises a first rigid lip; the second simple seal ofthe first fluid seal comprises a second rigid lip; the third simple sealof the first fluid seal comprises a third rigid lip; each of the firstrigid lip, the second rigid lip, and the third rigid lip is secured tothe housing element or to the rotor shaft; the gap of the first simpleseal of the first fluid seal between the first rigid lip and the housingelement or the rotor shaft; the second simple seal of the first fluidseal comprises a gap between the second rigid lip and the housingelement or the rotor shaft; and the third simple seal of the first fluidseal comprises a gap between the third rigid lip and the housing elementor the rotor shaft.